Magnetic resonance imaging apparatus and control method thereof

ABSTRACT

A magnetic resonance imaging apparatus includes a collection unit which applies a uniform static magnetic field to a subject and also applies a radio-frequency magnetic field and a gradient magnetic field to the subject in accordance with a predetermined pulse sequence to collect a magnetic resonance signal from the subject, a imaging unit which images the subject based on the magnetic resonance signal collected by the collection unit, a detection unit which detects a respiratory level of the subject, an informing unit which informs the subject of whether the detected respiratory level falls within an allowable range, and a unit which controls the collection unit and the imaging unit in such a manner that the magnetic resonance signal for imaging is collected and the subject is imaged based on the thus collected magnetic resonance signal for imaging when the detected respiratory level falls within the allowable range.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Applications No. 2007-122737, filed May 7, 2007;and No. 2008-018232, filed Jan. 29, 2008, the entire contents of both ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic resonance imaging apparatusthat obtains an image of a subject based on a nuclear magnetic resonance(NMR) signal emitted from the subject, and a control method thereof.

2. Description of the Related Art

To image a coronary artery based on the magnetic resonance image (MRI)method, a method of using a three-dimensional (3D) steady-state freeprecession (SSFP) sequence to perform imaging in a breath holding stateor a voluntary breathing state is used. In case of whole heart MRcoronary angiography (WH MRCA) where a course of a coronary artery of anentire heart is imaged in particular, holding a breath may lead to aninsufficient spatial resolution in some cases.

As a countermeasure, there is used an realtime motion correction (RMC)method of detecting a position of, e.g., a diaphragm based on an nuclearmagnetic resonance (NMR) signal under voluntary breathing to performimaging while monitoring a respiratory level and changing an imagingposition in accordance with this respiratory level.

However, a variable amount of the position that enables accurate imagingis restricted more or less, there is adopted a method of providing afixed threshold value with respect to a movement range obtained byrespiration and pausing collection of the NMR signal for imaging whenthe movement is large beyond this threshold value. That is, for example,a position of the diaphragm in a body axis direction can be detectedfrom a signal (which will be referred to as a monitor signal) obtainedby subjecting an NMR signal collected in relation to such a region R asshown in FIG. 1 to one-dimensional Fourier transformation. Since theposition of the diaphragm in the body axis direction cyclically moves upand down in accordance with respiration, plotting the cyclicallydetected positions of the diaphragm in time-series enables obtainingsuch a monitor signal as depicted in FIG. 2 that is synchronized with arespiratory motion. When a peak of this monitor signal is out of anallowable range between an upper threshold value USL and a lowerthreshold value LSL as shown in FIG. 2, imaging is not performed orcollected data is not used. When the monitor signal falls within theallowable range, data collection is carried out. Further, imaging iseffected while changing an imaging position in accordance with therespiratory motion.

Performing the operation in this manner enables excellently obtaining a3D image having a resolution that is high even under voluntarybreathing.

However, when the respiratory level is not fixed and gradually loweredor gradually increased and a portion of the signal obtained bysubjecting the NMR signal to one-dimensional Fourier transformation thatcorresponds to a position of the diaphragm deviates from the allowablerange as shown in, e.g., FIG. 3, an imaging time may become long, or anexamination may not be terminated in the worst case.

Therefore, as shown in, e.g., FIG. 4, a method of using a belt-likefixture which is a so-called abdominal belt 500 to fix an abdominal isused. This abdominal belt 500 enables obtaining a respiratory motionsuppressing effect to some extent.

However, even if the abdominal belt 500 is used to fix the abdominal,the respiratory motion cannot be completely suppressed, and therespiratory level may fluctuate to prolong an examination time inlong-time imaging. Furthermore, when fixing strength of the abdominalbelt 500 is increased to reduce the respiratory motion, a burden on asubject may be enlarged. When the examination is prolonged, the subjectmay start moving because of discomfort caused by fixing. Moreover, whenthe subject has a large body, even the abdominal belt cannot be used.

On the other hand, there is a multi breath holding method of repeatingbreath holding rather than voluntary breathing for a plurality of timesto image three-dimensional data.

As shown in FIG. 5, in the multi breath holding method, collection ofdata concerning one slab S1 including an entire heart is intermittentlyperformed in synchronization with repetitive breath holding performed bya subject. In addition, there is a method which additionally uses RMC inthe multi breath holding method and in which collection of data isperformed only when a monitor signal is within an allowable range.However, it is hard for the subject to correctly understand his or herrespiratory level. Even if the subject believes that he/she is uniformlyholding breath, the respiratory level fluctuates in breath holdingstates. Therefore, when RMC is additionally used, a monitor signal maynot fall within an allowable range even though the subject is holdingbreath, as shown in FIG. 6. In such a case, data is not collected eventhough the subject is holding breath, which imposes a load on thesubject. It should be noted that the inadequate breath holding statelengthens a period where data cannot be collected, and an efficiency fordata collection may be lowered, resulting in a long examination time.Additionally, when an imaging time is long, it is often the case thatthe subject gets tired of having to repeatedly hold his or her breath,the respiratory level in the breath holding state is fluctuates further,and an examination cannot be terminated in the worst case. In the multibreath holding state that does not additionally use RMC, the data on anumber of slabs is acquired in the state of different breath holdingpositions. As a result, reconstructed images may be discontinuous at theboundary between the slabs.

On the other hand, as shown in FIG. 7, there is considered a multi slabmethod of dividing a region including an entire heart into a pluralityof slabs S1 to S4 and individually collecting data from each of slabs S1to S4. To this case as well, either the simple multi breath holdingmethod or the multi breath holding method that additionally uses RMC isapplicable. FIG. 8 illustrates the case where the multi breath holdingmethod that additionally uses RMC is applied, and an allowable range ischanged in accordance with each slab. Since in this case the allowablerange differs depending upon the slabs, a fault is inevitably producedin each slab if the collected data is used for reconstruction withoutany correction. A similar fault is produced in the case where the simplemulti breath holding method is applied. The multi slab method has thefollowing problems. In the case of the multi breath holding method thatadditionally uses RMC, the breath holding positions vary, and thecollection of data cannot be performed efficiently, as in the above. Inthe case of the simple multi breath holding method, the breath holdingpositions vary each time, and blurring of each slab inevitably occurs.

As explained above, according to the voluntary breathing method, afluctuation in the respiratory level and the long-term variation of therespiratory level degrade an efficiency of data collection based on anavigator echo method.

Further, when a combination of the multi breath holding method and thesingle slab method is applied, blurring occurs due to each-timevariation of the breath holding position.

Where the multi breath holding method and the multi slab method areapplied in combination, the breath holding position varies each timedata is collected from one imaging region. However, the allowable rangechanges in accordance therewith, data is collected from differentpositions. Therefore, there is an inconvenience that a registrationerror is produced in a finally obtained 3D image and discontinuity ofdata occurs in this 3D image. Thus, to reduce such discontinuity, therespective slabs must be positioned in, e.g., image processing. However,since data positions included in the respective slabs are different fromeach other during data collection, appropriate positioning is difficult.

It is to be noted that relevant technologies are known from, e.g., JP-A2000-041970 (KOKAI), JP-A 2000-157507 (KOKAI), or JP-A 2004-057226.

BRIEF SUMMARY OF THE INVENTION

Under the circumstances, appropriately giving aid so that the subjectcan readily adapt his/her respiratory level to the allowable range hasbeen demanded.

Further, suppressing occurrence of a registration error or blurring ineach slab has been also demanded.

According to a first aspect of the present invention, there is provideda magnetic resonance imaging apparatus comprising: a collection unitwhich applies a uniform static magnetic field to a subject and alsoapplies a radio-frequency magnetic field and a gradient magnetic fieldto the subject in accordance with a predetermined pulse sequence tocollect a magnetic resonance signal from the subject; a imaging unitwhich images the subject based on the magnetic resonance signalcollected by the collection unit; a detection unit which detects arespiratory level of the subject; an informing unit which informs thesubject of whether the detected respiratory level falls within anallowable range; and a unit which controls the collection unit and theimaging unit in such a manner that the magnetic resonance signal forimaging is collected and the subject is imaged based on the thuscollected magnetic resonance signal for imaging when the detectedrespiratory level falls within the allowable range.

According to a second aspect of the present invention, there is provideda magnetic resonance imaging apparatus comprising: a collection unitwhich applies a uniform static magnetic field to a subject and alsoapplies a radio-frequency magnetic field and a gradient magnetic fieldto the subject in accordance with a predetermined pulse sequence toindividually collect each magnetic resonance signal from the subject inrelation to each of a plurality of slabs; a imaging unit which images animaging region containing the plurality of slabs based on the collectedmagnetic resonance signals; a unit which detects a respiratory level ofthe subject; a unit which controls the collection unit to collect themagnetic resonance signal when the detected respiratory level fallswithin an allowable range that is set with respect to each of theplurality of slabs; and a unit which sets the single allowable rangethat is applied in common to each of the plurality of slabs based on therespiratory level detected before the collection in relation to thefirst slab in the plurality of slabs begins.

According to a third aspect of the present invention, there is provideda display apparatus that is used with a magnetic resonance imagingapparatus that visualizes a subject based on a magnetic resonance signalcollected from the subject when a respiratory level of the subject fallswithin an allowable range, comprising: a generation unit which generatesan image indicating whether the respiratory level of the subject fallswithin the allowable range; and a display unit which displays the imageto the subject.

According to a fourth aspect of the present invention, there is provideda A control method of a magnetic resonance imaging apparatus, theapparatus comprising: a collection unit which applies a uniform staticmagnetic field to a subject and also applies a radio-frequency magneticfield and a gradient magnetic field to the subject in accordance with apredetermined sequence to collect a magnetic resonance signal from thesubject; and a imaging unit which images the subject based on themagnetic resonance signal collected by the collection unit, wherein themethod comprises: informing the subject of whether the detectedrespiratory levels falls within the allowable range; and controlling thecollection unit and the imaging unit to collect the magnetic resonancesignal and visualize the subject based on the thus collected magneticresonance signal when the detected respiratory level falls within theallowable range.

According to a fifth aspect of the present invention, there is provideda control method of a magnetic resonance imaging apparatus, theapparatus comprising: a collection unit which applies a uniform staticmagnetic field to a subject and also applies a radio-frequency magneticfield and a gradient magnetic field to the subject in accordance with apredetermined sequence to individually collect each magnetic resonancesignal from the subject in relation to each of a plurality of slabs; anda imaging unit which visualizes an imaging region containing theplurality of slabs based on the collected magnetic resonance signal,wherein the method comprises: detecting a respiratory level of thesubject; controlling the collection unit to collect the magneticresonance signal when the detected respiratory level falls within anallowable range that is set with respect to each of the plurality ofslabs; and setting the single allowable range that is applied in commonto each of the plurality of slabs based on the respiratory leveldetected before the collection with respect to the first slab in theplurality of slabs begins.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a view for explaining a conventional technology;

FIG. 2 is a view for explaining a conventional technology;

FIG. 3 is a view for explaining a conventional technology;

FIG. 4 is a view for explaining a conventional technology;

FIG. 5 is a view for explaining a conventional technology;

FIG. 6 is a view for explaining a conventional technology;

FIG. 7 is a view for explaining a conventional technology;

FIG. 8 is a view for explaining a conventional technology;

FIG. 9 is a view showing a structure of a magnetic resonance imagingapparatus (an MRI apparatus) according to a first embodiment of thepresent invention;

FIG. 10 is a view showing detailed structures of an image transmissionsystem and a display system in FIG. 9;

FIG. 11 is a view showing functions of mirrors in FIG. 10;

FIG. 12 is a view showing a setting example of slabs in the firstembodiment;

FIG. 13 is a view showing a setting example of an allowable range in thefirst embodiment;

FIG. 14 is a view showing an example of a sequence concerning collectionof an NMR signal;

FIG. 15 is a view showing a modified structural example of the displaysystem in FIG. 9;

FIG. 16 is a view showing a modified structural example of the displaysystem in FIG. 9;

FIG. 17 is a view showing modified structural examples of the imagetransmission system and the display system in FIG. 9;

FIG. 18 is a view showing an example of an image reproduction state inan LED array in FIG. 10 obtained by one-dimensionally aligning LEDs;

FIG. 19 is a view showing an example of an image reproduction state inthe LED array in FIG. 10 obtained by two-dimensionally aligning theLEDs;

FIG. 20 is a view showing an example of a structure of an optical cablegroup having an end portion functioning as a visualization unit sectionin FIG. 17;

FIG. 21 is a view showing a specific structural example of thevisualization unit in FIG. 17;

FIG. 22 is a view showing a fiber scope that can be used in place of theoptical cable group in FIG. 17;

FIG. 23 is a view showing a specific structural example of thevisualization unit in FIG. 17;

FIG. 24 is a view showing an arrangement example of the visualizationunit depicted in FIG. 23;

FIG. 25 is a view showing an arrangement example when a semitransparentoptical cable array is used as the visualization unit in FIG. 17;

FIG. 26 is a view showing a modified structural example of thevisualization unit;

FIG. 27 is a view showing modified structural example of the imagetransmission system and the display system in FIG. 9;

FIG. 28 is a view showing modified structural examples of the imagetransmission system and the display system in FIG. 9;

FIG. 29 is a view showing a modified structural example of an displaydevice in FIG. 10;

FIG. 30 is a view showing a relationship between a change in an actualrespiratory level and a monitored respiratory level;

FIG. 31 is a view sowing a structure of a magnetic resonance imagingapparatus according to each of second to fourth embodiments of thepresent invention;

FIG. 32 is a view showing an example of a first image in the secondembodiment;

FIG. 33 is a view showing an example of a second image in the secondembodiment;

FIG. 34 is a view showing a delay of a first respiratory level withrespect to a second respiratory level in the second embodiment;

FIG. 35 is a view showing an example of a display image immediatelybefore the first respiratory level is newly detected in the secondembodiment;

FIG. 36 is a view showing an example of a display image immediatelyafter the first respiratory level is newly detected in the secondembodiment;

FIG. 37 is a view showing a sequence when WH MRCA is performed in thethird embodiment;

FIG. 38 is a view showing an example of a display image in the thirdembodiment;

FIG. 39 is a view showing an example of a respiratory level detectionstate in the fourth embodiment; and

FIG. 40 is a view showing an example of a display image generated ateach time point in FIG. 39.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments according to the present invention will now be explainedhereinafter with reference to the accompanying drawings.

First Embodiment

FIG. 9 shows the configuration of a magnetic resonance imaging (MRI)apparatus, generally indicated at 100, according to a first embodiment.The MRI apparatus 100 includes a static field magnet 1, a gradient coil2, a gradient power supply 3, a bed 4, a bed controller 5, atransmission RF coil 6, a transmitter 7, a receiving RF coil 8, areceiver 9, a computer system 10, a image transmission system 11 and adisplay system 12.

The static field magnet 1 is formed in the shape of a hollow cylinderand adapted to generate a uniform static magnetic field within itsinside shape. As the static field magnet 1 use is made of a permanentmagnet, a superconducting magnet, or the like.

The gradient coil 2 is formed in the shape of a hollow cylinder andplaced inside the static field magnet 1. The gradient coil 2 is acombination of three coils each corresponding to a respective one of thethree mutually orthogonal X, Y and Z axes. When the three coils areindividually supplied with current from the gradient power supply 3, thegradient coil 2 generates gradient magnetic fields each of which has itsstrength varied along a corresponding one of the X, Y and Z axes.Suppose that the Z-axis direction coincides with the direction of thestatic magnetic field. The gradient magnetic fields in the X, Y andZ-axis directions are used as a slice selecting gradient field Gs, aphase encoding gradient magnetic field Ge, and a readout gradientmagnetic field Gr, respectively. The slice selecting gradient magneticfield Gs is used to arbitrarily determine an imaging plane section. Thephase encoding gradient magnetic field Ge is used to change the phase ofNMR signals according to spatial location. The readout gradient magneticfield Gr is used to change the frequency of the NMR signals according tospatial location.

A subject 200 under examination is laid down on a top board 4 a of thebed 4 and moved into the space of the gradient coil 2. The top board 4 ais driven by the bed controller 5 to move in its lengthwise directionand in an up-and-down direction. Usually, the bed 4 is installed so thatits lengthwise direction is parallel to the central axis of the staticfield magnet 1.

The transmitting RF coil 6 is placed inside the gradient coil 2 andgenerates a radio-frequency magnetic field in response to applicationthereto of a radio-frequency pulse from the transmitter 7.

The transmitter 7 has an oscillator, a phase selector, a frequencyconverter, an amplitude modulator, a radio-frequency power amplifier,etc., built in and transmits radio-frequency pulses corresponding toLarmor frequency to the transmitting RF coil 6.

The receiving RF coil 8 is placed inside the gradient coil 2 and adaptedto receive NMR signals emitted from the subject under examinationsubjected to the radio-frequency magnetic field. The output signal fromthe receiving RF coil 8 is applied to the receiver 9.

The receiver 9 produces NMR signal data on the basis of the outputsignal of the receiving RF coil 8.

The computer system 10 includes an interface unit 10 a, a datacollection unit 10 b, a reconstruction unit 10 c, a memory unit 10 d, adisplay unit 10 e, an input unit 10 f, and a main controller 10 g.

The interface unit 10 a is connected to the gradient power supply 3, thebed controller 5, the transmitter 7, the receiving RF coil 8, and thereceiver 9 and allows signals to be transferred between each of thesecomponents and the computer system 10.

The data collection unit 10 b collects via the interface unit 101digital signals output from the receiver 9 and then stores the collecteddigital signals, i.e., the NMR signal data, into the memory unit 10 d.

The reconstruction unit 10 c performs postprocessing, i.e.,reconstruction, such as Fourier transforms, on NMR signals data storedin the storage unit 10 d to obtain spectrum data of desired nuclearspins within the subject 200 or image data.

The memory unit 10 d stores NMR signal data and spectrum data or imagedata for each subject.

The display unit 10 e displays a variety of information, such asspectrum data, image data, etc., under the control of the maincontroller 10 g. As the display unit 10 e there is available a displaydevice, such as a liquid crystal display.

The input unit 10 f receives a variety of commands and informationinputs from an operator. As the input unit 10 f there is available apointing device, such as a mouse or trackball, a selection device, suchas a mode changeover switch, or an input device, such as a keyboard.Further, the input unit 10 f accepts a specification from the operatorof an excitation slice or an excitation slice or an excitation slabincluding an imaging region of, e.g., an entire heart or a target partsuch as a diaphragm.

The main controller 10 g has a non-illustrated CPU, a memory, andothers, and collectively controls the MRI apparatus 100. Furthermore,the main controller 10 g generates an image signal of an imageindicating whether a respiratory level falls within the allowable range.This image signal is, e.g., an NTSC (national television systemcommittee) signal.

The image transmission system 11 optically transmits the image signalgenerated by the main controller 10 a.

The display system 12 displays an image based on the image signal sothat a subject 200 set in an imaging state can visually recognize theimage.

FIG. 10 is a view showing detailed structures of the image transmissionsystem 11 and the display system 12. It is to be noted that likereference numerals denote parts equal to those in FIG. 9, therebyomitting a detailed explanation thereof.

The image transmission system 11 includes an electric-optical signalconverter 11 a, an optical cable (an optical fiber cable) 11 b, and anoptical-electrical signal converter 11 c. The display system 12 includesan display device 12 a and a mirror 12 b.

Reference number 20 in FIG. 10 denotes a gantry. The gantry 20accommodates the static field magnet 1, the gradient coil unit 2, andthe transmission RF coil 6. The gantry 20 has a substantiallycylindrical imaging space 20 a having a central axis matching with acylindrical central axis defined by the static field magnet 1 therein,and openings 20 b and 20 c from which this imaging space 20 a is openedto the outside of the gantry 20 are formed at both ends of the imagingspace. The bed 4 is arranged on the side of the one opening 20 b inclose proximity to the gantry 20. Furthermore, the bed 4 supplies thetop board 4 a from the opening 20 b into the imaging space 20 a.Therefore, the opening 20 b will be referred to as a bed-side opening 20b and the opening 20 c will be referred to as a contra-bed-side opening20 c hereinafter.

The gantry 20 and the bed 4 are arranged in a magnetically shieldedshield room R1. The computer system 10 is arranged in an operation roomR2 different from the shield room R1.

The electric-optical signal converter 11 a is arranged outside theshield room R1, i.e., in the operation room R2 in this example. Theelectric-optical signal converter 11 a converts an image signal outputas an electrical signal from the interface unit 10 a into an opticalsignal.

The optical cable 11 b transmits an image signal output as the opticalsignal from the electric-optical signal converter 11 a to theoptical-electric signal converter 11 c.

The optical-electric signal converter 11 c is arranged in the shieldroom R1. The optical-electric signal converter 11 c converts an imagesignal transmitted as the optical signal through the optical cable 11 binto an electrical signal.

Thus, the image transmission system 11 transmits the image signal as theoptical signal to the shield room R1.

The display device 12 a is arranged in the shield room R1. The displaydevice 12 a displays an image indicated by the image signal output asthe electric signal from the optical-electric signal converter 11 c. Thedisplay device 12 a is arranged on the contra-bed-side opening 20 c sidein a posture that a display plane thereof becomes substantiallyorthogonal to the central axis of the imaging space 20 a and also facesthe imaging space 20 a. As the display device 12 a, a known displaydevice, e.g., a liquid crystal monitor can be utilized. However, thedisplay device 12 a includes, e.g., an electromagnetic shield to preventnoise produced therein from leaking into the shield room R1.

The mirror 12 b is arranged in the imaging space 20 a. The mirror 12 breflects an image displayed in the display device 12 a as shown in FIG.11 so that the subject 200 lying down on the top board 4 a and carriedinto the imaging space 20 a can visually recognize the image displayedin the display device 12 a without changing his/her posture.

An operation of the thus configured MRI apparatus 100 will now beexplained.

In this MRI apparatus 100, at the time of WH MRCA, data collection iscarried out based on a multi slab/multi breath holding method. That is,for example, as shown in FIG. 12, a region including an entire heart isdivided into a plurality of slabs S1 to S4, and data collection isindividually performed in each of these slabs S1 to S4. Furthermore,like the conventional technology, this data collection is executed whena level of a monitor signal obtained by subjecting an NMR signalacquired from a periphery of a diaphragm or a liver to one-dimensionalFourier transformation falls within an allowable range between an upperthreshold value USL and a lower threshold value LSL.

However, in the first embodiment, as shown in FIG. 13, the maincontroller 10 g applies the upper threshold value USL and the lowerthreshold value LSL determined based on a respiratory level of thesubject 200 before data collection in the first slab S1 to all of theslabs S1 to S4 without change. As to settings of the upper thresholdvalue USL and the lower threshold value LSL, the subject 200 is urged tonaturally breathe for several times before scanning in order tostatistically obtain, e.g., a mode value of the respiratory level, andthe threshold values can be set so that a preset allowable margin (e.g.,5 mm) can be acquired with the mode value as a reference (at thecenter). The upper threshold value USL and the lower threshold value LSLmay be set by an operator or may be automatically set under control ofthe main controller 10 g. At this time, the respiratory level of thesubject 200 may be judged by using the NMR signal or a signal of arespiratory synchronizer (e.g., a bellows).

FIG. 14 is a view showing an example of a sequence concerning collectionof the NMR signal.

This imaging method is usually carried out with electrocardiographicsynchronization. Furthermore, after a fixed delay time passes from an Rwave, a motion probing pulse (MPP) is collected as the NNR signal toobtain the monitor signal. This collection of the MPP is carried outwithout applying a phase encoding gradient magnetic field Ge. Moreover,after collecting the MPP, data collection for imaging is performed. Inthis data collection for imaging, the phase encoding gradient magneticfield Ge is applied.

On the other hand, during execution of WH MRCA in such a conformation,the main controller 10 g generates an image indicating whether therespiratory level of the subject 200 falls within the allowable range.The image is, e.g., such an image as depicted in FIG. 13 showing themonitor signal, the upper threshold value USL, and the lower thresholdvalue LSL. The main controller 10 g displays this image in the displayunit 10 e to allow an operator to confirm. Additionally, the maincontroller 10 g supplies an image signal indicating the image to theelectric-optical signal converter 11 a through the interface unit 10 a.This image signal is converted into an optical signal by theelectric-optical signal converter 11 a to be transmitted through theoptical cable 11 b, and led into the shield room R1. Further, the imagesignal is again converted into an electric signal by theoptical-electric signal converter 11 c in the shield room R1 to besupplied to the display device 12 a. Thus, the display device 12 adisplays the image indicated by this image signal. The image displayedin the display device 12 a is reflected by the mirror 12 b to bevisually recognized by the subject 200.

Therefore, the subject 200 can confirm whether his/her respiratory levelat the present time falls within the allowable range by confirmingreflection of the image in the mirror 12 b. Furthermore, the subject 200can hold breathing in a state where his/her respiratory level fallswithin the allowable range.

Thus, in the MRI apparatus 100, data collection can be assuredlyperformed every time the subject 200 holds breathing, thereby improvingan efficiency of data collection. Moreover, since data collected everytime breathing is held can be obtained in a respiratory state in thefixed allowable range in each of the plurality of slabs, a 3D imagefinally obtained based on data collected with respect to each of theplurality of slabs is a high-quality image with less registration erroror blurring.

Additionally, in the MRI apparatus 100, the image signal generatedoutside the shield room R1 is led into the shield room R1 as the opticalsignal. As a result, noise and others from the shield room R1 can beprevented from affecting collection of the NMR signal.

Second to Fourth Embodiments

Meanwhile, in the first embodiment, collection of the NMR signal foracquisition of positional information is performed only once per heartrate. That is, the respiratory level is monitored only once or twice perrespiration as shown in FIG. 30, the subject may not recognize a changein respiration even if the subject is informed of the monitoredrespiratory level alone. That is, a interval of updating informationacquired in the above-explained cycle may be too long as a interval ofupdating information required to control the respiratory level. In otherwords, a feedback time constant in respiratory level control is long.

Under such circumstances, it can be considered that adjustment of therespiratory level by the subject based on the monitored respiratorylevel is similar to a case where the feedback time constant in automaticcontrol is long, and under-control or over-control may possibly occur.

Thus, second to fourth embodiments that avoid such an inconvenience willnow be explained hereinafter.

FIG. 31 is a view showing a structure of a magnetic resonance imagingapparatus (an MRI apparatus) 300 according to each of the second tofourth embodiments. It is to be noted that, in FIG. 31, like referencenumbers denote parts equal to those in FIG. 9, thereby omitting adetailed explanation thereof.

The MRI apparatus 300 includes a static field magnet 1, a gradient coilunit 2, a gradient power supply 3, a bed 4, a bed controller 5, atransmitting RF coil 6, a transmitter 7, a receiving RF coil 8, areceiver 9, a computer system 10, an image transmission system 1, adisplay system 12, and a respiratory synchronization sensor 13.

That is, the MRI apparatus 300 includes the respiratory synchronizationsensor 13 in addition to the respective elements included in the MRIapparatus 100.

The respiratory synchronization sensor 13 is disposed to an abdominal ofa subject 200 to detect a respiratory level of the subject 200 based ona physical movement of the abdominal of the subject 200.

Second Embodiment

A main controller 10 g in the second embodiment includes a plurality offunctions mentioned below. It is to be noted that the plurality offunctions can be realized by allowing a processor included in the maincontroller 10 g to execute a program.

As one of the functions, each relevant section is controlled to enable adata collection unit 10 b to obtain an NMR signal required to detect arespiratory level of the subject 200 (which will be referred to as amonitoring NMR signal hereinafter). As one of the functions, therespiratory level of the subject 200 is detected based on the monitoringNMR signal acquired by the data collection unit 10 b. As one of thefunctions, each relevant section is controlled to enable the datacollection unit 10 b to collect an NMR signal required to reconstruct animage (which will be referred to as a reconstruction NMR signalhereinafter) when the respiratory level detected based on the monitoringNMR signal falls within an allowable range. As one of the functions, adisplay image obtained by combining a respiratory waveform representinga change in the respiratory level detected by the respiratorysynchronization sensor 13 with an image indicating the respiratory leveldetected based on the monitoring NMR signal is generated. It is to benoted that the respiratory level detected based on the monitoring NMRsignal will be referred to as a first respiratory level and therespiratory level detected by the respiratory synchronization sensor 13will be referred to as a second respiratory level hereinafter.

In this MRI apparatus 300 according to the second embodiment, WH MRCA isexecuted based on a known sequence. During such WH MRCA, the maincontroller 10 g generates a display image that informs the subject 200of whether the respiratory level of the subject 200 falls within theallowable range as follows. It is to be noted that, in WH MRCA, themonitoring NMR signal is acquired. The monitoring NMR signal is an NMRsignal collected from an excitation slice or an excitation slabincluding a target part such as a diaphragm. The monitoring NMR signalcan be acquired without applying, e.g., a phase encoding gradientmagnetic field. As the monitoring NMR signal, an MPP can be used likethe first embodiment, for example.

The main controller 10 g acquires the second respiratory level detectedby the respiratory synchronization sensor 13 at a rate that issufficient to reproduce a respiratory waveform. It is to be noted thatthe respiratory synchronization sensor 13 can continuously detect therespiratory level in an actual time by using, e.g., a bellows.

The main controller 10 g detects the first respiratory level once perheart rate in control for WH MRCA. The main controller 10 g generatessuch a first image as shown in FIG. 32 in which each first aspiratorylevel acquired in a recent fixed period is arranged on a plane definedby a time axis and a respiratory level axis.

On the other hand, the main controller 10 g generates such a secondimage as shown in FIG. 33 representing a respiratory waveform in theperiod based on the second respiratory level acquired in the fixedperiod.

Further, the main controller 10 g generates a display image as an imageobtained by combining the first image with the second image. At thistime, the main controller 10 g normalizes respective amplitude scales (amaximum value and a minimum value of each amplitude) of the firstrespiratory level and the second respiratory level to be combined witheach other.

The main controller 10 g updates the display image every time the secondaspiratory level is acquired. Thus, the display image is an image inwhich the respiratory waveform scrolls with elapse of time.

Meanwhile, since the monitoring NMR signal is acquired and the firstrespiratory level is obtained based on this monitoring NMR signal,detection of the first respiratory level requires a slight amount oftime. Therefore, detection of the first respiratory level has actualtime properties lower than those of detection of the second respiratorylevel. Therefore, as shown in FIG. 34, the first respiratory level has afixed delay with respect to the second respiratory level. Thus, the maincontroller 10 g combines the first image with the second image tocorrect this delay.

That is, it is assumed that a display image immediately before the firstrespiratory level is newly detected is as shown in FIG. 35. Furthermore,when updating the display image after the first respiratory level isnewly detected, the display image is updated in such a manner that thenewly detected respiratory level is not displayed as information at thepresent time but it is displayed as information at a time point reachedby traveling back in time by an amount corresponding to the delay asshown in FIG. 36.

The thus generated display image is transmitted to the display system 12through the interface unit 10 a and the image transmission system 11,and this display system 12 displays this display image so that thesubject 200 can visually recognize.

As explained above, according to the second embodiment, in the displayimage, the first respiratory level detected based on the monitoring NMRsignal and the second respiratory level detected based on therespiratory synchronization sensor 13 are simultaneously shown.Therefore, the subject 200 can recognize a state of a change in therespiratory level based on the respiratory waveform in this displayimage and an accurate respiratory level based on display of the secondrespiratory level. As a result, the subject 200 can accurately grasp anactual state of respiration, thereby appropriately adjustingrespiration.

Third Embodiment

In the third embodiment, a main controller 10 g includes a plurality offunctions mentioned below. It is to be noted that the plurality offunctions can be realized by allowing a processor included in the maincontroller 10 g to execute a program.

As one of the functions, relevant respective sections are controlled sothat a data collection unit 10 b can acquire a monitoring NMR signal. Asone of the functions, a first respiratory level is detected based on themonitoring NMR signal. As one of the functions, relevant respectivesections are controlled so that the data collection unit 10 b cancollect a reconstruction NMR signal when the respiratory level detectedbased on the monitoring NMR signal falls within an allowable range. Asone of the functions, relevant respective sections are controlled sothat the data collection unit 10 b can acquire an NMR signal that isused to detect a respiratory level for display (which will be referredto as a display NMR signal hereinafter). As one of the functions, arespiratory level of a subject 200 (which will be referred to as asecond respiratory level hereinafter) is detected based on the displayNMR signal. As one of the functions, a display image indicating thefirst respiratory level and the second respiratory level is generated.

In the MRI apparatus 300 according to the third embodiment, whenexecuting WH MRCA, the main controller 10 g allows the data collectionunit 10 b to collect the NMR signal based on such a sequence as depictedin FIG. 37.

In the sequence shown in FIG. 37, a plurality of MPPs are collected inone heart rate. The plurality of MPPs are classified into a main MPP anda sub-MPP. The main PP is collected immediately before a data collectionperiod in an imaging region. The sub-MPP is collected at a timingdifferent from that of the main MPP while avoiding the data collectionperiod. The sub-MPP may be collected either before or after the main MPPin any period excluding the data collection period in the imagingregion. For example, the plurality of sub-MPPs may be collected beforethe main MPP. Further, the plurality of MPPs may be collected at equalintervals within one heart rate (including not only the sub-MPP but alsothe main MPP). In this case, when any one of the plurality of MPPs setat equal intervals is included in the data collection period in theimaging region, this MPP is not collected.

The main MPP corresponds to the MPP acquired in the sequence depicted inFIG. 14, and it is used as the monitoring NMR signal. The sub-MPP isadded and acquired irrespective of the purpose of control of WH MRCA,and it is used as the display NMR signal.

Furthermore, the main controller 10 g detects the first respiratorylevel for WH MRCA based on the monitoring NMR signal alone. The maincontroller 10 g detects the second respiratory level likewise based onthe display NMR signal, though this signal is not used for WH MRCA.Moreover, the main controller 10 g generates, e.g., such a display imageas depicted in FIG. 28 in which the first respiratory level and thesecond respiratory level acquired in a recent fixed period arerespectively arranged on a plane defined by a time axis and arespiratory level axis.

The thus generated display image is transmitted to a display system 12through an interface unit 10 a and an image transmission system 11, andthis display system 12 displays this display image in a state where thesubject 200 can visually recognize it.

As explained above, according to the third embodiment, in the displayimage, many respiratory levels respectively detected in a short periodare shown in time-series. Therefore, the subject 200 can recognize astate of a change in the respiratory level from this display image. As aresult, the subject 200 can accurately grasp an actual state ofrespiration, thereby appropriately adjusting respiration.

Fourth Embodiment

In the fourth embodiment, a main controller 10 g includes a plurality offunctions mentioned below. It is to be noted that the plurality offunctions can be realized by allowing a processor included in the maincontroller 10 g to execute a program.

As one of the functions, relevant respective sections are controlled sothat a data collection unit 10 b can collect a monitoring NMR signal. Asone of the functions, a respiratory level of a subject 200 is detectedbased on the monitoring NMR signal. As one of the functions, relevantrespective sections are controlled so that the data collection unit 10 bcan collect a reconstruction NMR signal when the respiratory leveldetected based on the monitoring NMR signal falls within an allowablerange. As one of the functions, a display image showing the latestdetected respiratory level and a maximum value of detection levelsdetected within a predetermined period is generated.

In the MRI apparatus 300 according to the fourth embodiment, WH MRCA isexecuted in accordance with a known sequence. During execution of suchWH MRCA, the main controller 10 g generates a display image that informsthe subject 200 of whether the respiratory level of the subject 200falls within the allowable range as follows.

The main controller 10 g detects the respiratory level once per heartrate in control for WH MRCA. The main controller 10 g generates adisplay image indicating a detected respiratory level every time therespiratory level is newly detected.

For example, as shown in FIG. 39, the main controller 10 g generatessuch a display image IA as depicted in FIG. 40 in accordance withdetection of such a respiratory level as depicted in FIG. 39 at a timepoint TA. In the display image IA, the respiratory level detected at thetime point TA is indicated by a black dot.

On the other hand, in accordance with detection of such a respiratorylevel as depicted in FIG. 39 at a time point TB, the main controller 10g generates a display image IB in which the respiratory level detectedat the time point TB is indicated by the black dot as shown in FIG. 40.Meanwhile, the detection level detected at the time point TB is lowerthan the detection level detected at the time point TA. In such a case,the main controller 10 g indicates the detection level detected at thetime point TA as a recent maximum level in the display image IB. It isto be noted that the maximum level is indicated as a dot with hatchingin FIG. 40.

In accordance with detection of such a respiratory level as shown inFIG. 39 at time point TC, the main controller 10 g generates a displayimage IC in which the respiratory level detected at a time point TC isindicated by the black dot as shown in FIG. 40. Since the respiratorylevel detected at the time point TC is higher than the maximum levelobtained thus far, the maximum level is not shown in the display imageIC.

Thereafter, display images ID to IF in FIG. 40 are likewise generated attime points TD to TF in FIG. 39, respectively.

In accordance with detection of such a respiratory level as shown inFIG. 39 at a time point TG, the main controller 10 g generates a displayimage IG in which the respiratory level detected at the time point TG isindicated by the black dot as depicted in FIG. 40. Meanwhile, themaximum level obtained thus far is the respiratory level detected at thetime point TC but, at the time point TG, a specified time T1 or moreelapses from the time point TC. In such a case, the main controller 10 gcancels the last maximum level, and does not show this level in a newlygenerated image.

Thereafter, display images IH to IJ in FIG. 40 are likewise generated attime points TH to TJ in FIG. 39, respectively.

The thus generated display images are transmitted to a display system 12through an interface unit 10 a and an image transmission system 11, andthis display system 12 sequentially displays these display images in astate where the subject 200 can visually recognize them.

As explained above, according to the fourth embodiment, the latestdetected respiratory level and a maximum respiratory level detected in arecent fixed period are shown in the display image. Therefore, thesubject 200 can recognize from this display image a relationship betweenthe current respiratory level and the recent maximum level. As a result,the subject 200 can accurately grasp an actual state of respiratory,thereby appropriately adjusting respiration.

Each of the foregoing embodiments can be modified in many ways asfollows.

(1) In each embodiment, the image signal may be generated by using,e.g., a CCD (charge-coupled device) camera to image a picture displayedin the display unit 10 e.

(2) In each embodiment, as indicated by a broken line in FIG. 10, thedisplay device 12 a may be arranged on the bed-side opening 20 b side ina posture that the display plane thereof becomes substantiallyorthogonal to the central axis of the imaging space 20 a and faces theimaging space 20 a. Alternatively, the display device 12 a may bearranged on the bed-side opening 20 b side in a posture that the displayplane thereof becomes substantially parallel to the central axis of theimaging space 20 a. When the display device 12 a is arranged in theposture that the display plane thereof becomes substantially parallel tothe central axis of the imaging space 20 a, the mirror 12 c reflects animage displayed in the display device 12 a toward the mirror 12 b.However, when the display device 12 a is arranged on the bed-sideopening 20 b side, a direction of the mirror 12 b is changed asindicated by a broken line in FIG. 11. The direction of the mirror 12 bmay be fixed or may be variable.

(3) In each embodiment, a large-screen display (e.g., a liquid crystalor a plasma) 12 d may be used in place of the display device 12 a asshown in FIG. 15.

(4) In each embodiment, a projector 12 e may be used in place of thedisplay device 12 a as shown in FIG. 16 to project an image indicated bythe image signal onto a wall of the shield room R1. When using theprojector 12 e, an image may be directly projected onto the mirror 12 b,or the mirror 12 b may be omitted to project an image onto a wallsurface of the gantry 20 around the imaging space 20 a. A plottingdevice obtained by combining a laser emitting device and a movablemirror may be used in place of the display device 12 a and the mirror 12b to plot an image on the wall surface of the gantry 20.

(5) In each embodiment, the display device 12 a my be arranged in theimaging space 20 a. In this case, the mirror 12 b may be omitted toallow the subject 200 to directly visually observe an image displayed inthe display device 12 a. Further, in this case, disposing a liquidcrystal sheet or an organic electroluminescent (EL) panel on the wallsurface of the gantry 20 around the imaging space 20 a can beconsidered.

(6) In each embodiment, an image generated outside the shield room R1may be led into the shield room R1 to be visually observed by thesubject 200.

For example, as shown in FIG. 17, the image transmission system 11 isconfigured to include a light-emitting diode (LED) array 11 d and anoptical cable group (an optical fiber group) 11 e, and the displaysystem 12 is configured to include a visualization unit 12 f.

The LED array 11 d has many LEDs one-dimensionally or two-dimensionallyarranged therein, and reproduces an image indicated by the image signal.The optical cable group 11 e is obtained by bundling many opticalcables, and transmits the image reproduced by the LED array 11 d as itis. The visualization unit 12 f allows the subject to visually observethe image transmitted through the optical cable group 11 e.

FIG. 18 is a view showing an example of a reproduction state of an imagein the LED array 11 d having the LEDs one-dimensionally arrangedtherein. It is to be noted that one circle in FIG. 18 represents oneLED. In FIG. 18, turning on the LEDs at both ends in a blue color or ayellow color represents the upper threshold value USL and the lowerthreshold value LSL, and turning one of the five inner LEDs in a redcolor represents a current level of a current monitor signal. When thecurrent level of the monitor signal is out of the allowable range, noneof the five inner LEDs is turned on.

FIG. 19 is a view showing an example of a reproduction state of an imagein the LED array 11 d having the LEDs two-dimensionally arrangedtherein. It is to be noted that one circle in FIG. 19 represents oneLED. In FIG. 19, four LED strings each having an alignment depicted inFIG. 18 are arranged. A change in level of the monitor signal isrepresented by using each of the four LED strings like the aboveexample.

When facets of many optical cables included in the optical cable group11 e are one-dimensionally or two-dimensionally arranged, thevisualization unit 12 f can be configured to visualize an image by usingan alignment of lights emitted from these optical cables.

FIG. 20 is a view showing an example of a structure of the optical cablegroup 11 e having an end portion functioning as the visualization unit12 f.

Alternatively, the visualization unit 12 f may be arranged in theimaging space 20 a as shown in FIG. 21 to project an image onto the wallsurface of the gantry 20 on the upper side of the imaging space 20 a.

Alternatively, such a fiber scope 11 f as shown in FIG. 22 may be usedin place of the optical cable group 11 e to guide an image reproduced bythe LED array 11 d to eyes of the subject 200.

Such a semitransparent optical cable array as shown in FIG. 23 may beused as the visualization unit 12 f, and it may be disposed on the wallsurface of the gantry 20 on the upper side of the imaging space 20 a asdepicted in FIG. 24.

The semitransparent optical cable array as the visualization unit 12 fmay be arranged to match an arrangement direction of the semitransparentoptical cable to a circumferential direction of the wall surface of thegantry around the imaging space 20 a as depicted in FIG. 25.

The visualization unit 12 f may be configured like glasses in which endportions of the optical cable groups 11 e are arranged in lens portionsas shown in FIG. 26, and this unit may be put on a face of the subject200.

(7) In each embodiment, the image transmission technology explained in(6) may be used to lead an image displayed in the display unit 10 e oran image displayed in the display device 12 a to the imaging space 20 a,thereby allowing the subject 200 to visually observe the image.

In this case, as shown in FIG. 27, an input end of the optical cablegroup 11 e is appressed against the display unit 10 e or the displaydevice 12 a to enable incidence of an upper part of the image displayedin the display unit 10 e or the display device 12 a without loss. Atthis time, using a lens or an auxiliary optical guide medium is alsouseful. Furthermore, a glass with a lens or a diffusion glass ispreferable as the visualization unit 12 f.

Moreover, when using the fiber scope 11 f in place of the optical cablegroup 11 e, as shown in FIG. 28, an image displayed in the display unit11 e or the display device 12 a is reduced in size by a reducing lens 11g to enter the fiber scope 11 f, and the image exiting the fiber scope11 f is expanded by a magnifying lens 11 h to enter the visualizationunit 12 f.

(8) In each embodiment, the display device 12 a may be configured likeglasses having the LED arrays 12 g contained in lens portions as shownin FIG. 29, and this unit may be put on the face of the subject 200.

(9) In the first embodiment, several respiratory patterns may beregistered as ideal states in advance, and one of these patterns may beused as a guide pattern to display an image that can show this patternand a measured actual respiratory pattern in comparison with each other.As a result, the subject 200 can be guided to approximate a respiratorypattern of the subject 20 to the ideal pattern. That is, a so-calledexternal guiding method can be appropriately executed. It is to be notedthat the guide pattern and the measured pattern may be displayed indifferent colors. Additionally, an HR (a heart rate) when the subject200 is at rest may be measured in advance, and a respiratory patternthat enables stably and rapidly terminating data collection may beselected as a guide pattern by using this HR as a reference.

(10) In each embodiment, display of an image indicating whether therespiratory level falls within the allowable range is effective whenapplied to a situation using a method other than the multi slab/multibreath holding method, i.e., a voluntary breathing method or a singleslab/multi breath holding method as long as it is a method of performingdata collection when the respiratory level falls within the allowablerange.

(11) In each embodiment, a movement correction method of tracing animaging region of a heart while tracing a movement of a diaphragm may bealso used. When this method is used, since a fluctuation in therespiratory level in the allowable range can be corrected by themovement correction method to highly accurately match positions of multislabs, a registration error or blurring in a 3D image can be furtherreduced.

(12) In the first embodiment, the image transmission system 11 and thedisplay system 12 can be used to inform the subject 200 of various kindsof information except information indicating whether the respiratorylevel falls within the allowable range.

(13) In each embodiment, the image transmission system 11 may lead theimage signal that is kept as the electrical signal into the shield roomR1.

(14) In the second embodiment, normalization or delay correction doesnot have to be performed.

(15) In the third embodiment, the number of times of acquisition of thesub-MPP per heart rate may be an arbitrary number of times that is equalto or above 1.

(16) In the third embodiment, when acquisition of the sub-MPP isperformed more than once per heart rate, the respiratory level judgedbased on the main MPP does not have to be included in the display image.

(17) In the fourth embodiment, when the maximum level and therespiratory level at the present time are displayed in differentconformations so that they can be respectively displayed even thoughboth the levels coincide with each other, the subject 200 can furthereasily understand that the maximum level and the respiratory level atthe present time coincide with each other. This can be realized by achange, e.g., showing the maximum level in the form of a horizontalline.

(18) In each embodiment, specific contents of the display image can bearbitrarily changed.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A magnetic resonance imaging apparatus comprising: a collection unitwhich applies a uniform static magnetic field to a subject and alsoapplies a radio-frequency magnetic field and a gradient magnetic fieldto the subject in accordance with a predetermined pulse sequence tocollect a magnetic resonance signal from the subject; a imaging unitwhich images the subject based on the magnetic resonance signalcollected by the collection unit; a detection unit which detects arespiratory level of the subject; an informing unit which informs thesubject of whether the detected respiratory level falls within anallowable range; and a unit which controls the collection unit and theimaging unit in such a manner that the magnetic resonance signal forimaging is collected and the subject is imaged based on the thuscollected magnetic resonance signal for imaging when the detectedrespiratory level falls within the allowable range.
 2. The magneticresonance imaging apparatus according to claim 1, wherein the detectionunit performs: setting an excitation slice or an excitation slab in atarget part that is present in the subject; controlling the collectionunit to collect the magnetic resonance signal for positional detectionfrom the excitation slice or the excitation slab without applying aphase encoding gradient magnetic field as one component of the gradientmagnetic field; acquiring positional information of the target partbased on the magnetic resonance signal for positional detectioncollected by the collection unit; and detecting the respiratory levelbased on the acquired positional information.
 3. The magnetic resonanceimaging apparatus according to claim 2, wherein the detection unitdetermines a diaphragm as the target part.
 4. The magnetic resonanceimaging apparatus according to claim 2, wherein the detection unitcontrols the collection unit to collect the magnetic resonance signalfor positional detection without applying the phase encoding gradientmagnetic field per heart rate of the subject immediately before thecollection unit collects the magnetic resonance signal for imaging withapplication of the phase encoding gradient magnetic field.
 5. Themagnetic resonance imaging apparatus according to claim 1, wherein thedetection unit detects the respiratory level at each predetermined time,and the informing unit informs the subject of a relationship between thelatest respiratory level detected by the detection unit andpredetermined threshold information.
 6. The magnetic resonance imagingapparatus according to claim 1, further comprising a unit which correctsthe magnetic resonance signal for imaging collected by the collectionunit to reduce an influence of a fluctuation in the respiratory level.7. The magnetic resonance imaging apparatus according to claim 1,wherein the informing unit comprises: a generation unit which isarranged in a second room different from a magnetically shielded firstroom where the collection unit is arranged, and generates an imageindicating whether the detected respiratory level falls within theallowable range; a transmission unit which optically transmits the imagefrom the second room to the first room; and a display unit which isarranged in the first room and displays the image transmitted throughthe transmission unit to the subject.
 8. The magnetic resonance imagingapparatus according to claim 7, wherein the generation unit generatesimage information indicative of the image, the transmission unittransmits the image information by using an optical signal, and thedisplay unit reproduces and displays the image based on the imageinformation.
 9. The magnetic resonance imaging apparatus according toclaim 7, wherein the generation unit generates the image as a visiblelight image, the transmission unit transmits the visible light image,and the display unit projects the visible light image to eyes of thesubject.
 10. The magnetic resonance imaging apparatus according to claim1, wherein the detection unit controls the collection unit to collectthe magnetic resonance signal for respiratory level detection at atiming different from that of the magnetic resonance signal for imaging,the detection unit detects a respiratory level of the subject as a firstrespiratory level based on the magnetic resonance signal for respiratorylevel detection collected by the collection unit, the detection unitfurther detects a respiratory level of the subject as a secondrespiratory level based on a physical movement of the subject involvedby respiration, the informing unit generates a display image that is acombination of a graph showing a change in the second respiratory leveland an image indicating the first respiratory level, and the informingunit further displays the display image to the subject.
 11. The magneticresonance imaging apparatus according to claim 10, wherein the informingunit generates a display image that is a combination of a graph showinga change in the normalized second respiratory level and an imageindicating the normalized first respiratory level.
 12. The magneticresonance imaging apparatus according to claim 10, wherein the informingunit combines the graph with the image to generate the display imagewhile correcting a difference between times required for the first andsecond detection units to detect the first and second respiratorylevels, respectively.
 13. The magnetic resonance imaging apparatusaccording to claim 1, wherein the detection unit controls the collectionunit to collect the magnetic resonance signal for first respiratorylevel detection at a timing different from that of the magneticresonance signal for imaging, the detection unit detects a firstrespiratory level that is used to confirm whether a respiratory level ofthe subject falls within the allowable range based on the magneticresonance signal for first respiratory level detection collected by thecollection unit, the detection unit controls the collection unit tocollect the magnetic resonance signal for second respiratory leveldetection at a timing different from those of the magnetic resonancesignals for imaging and for first respiratory level detection, thedetection unit further detects a second respiratory level of the subjectbased on the magnetic resonance signal for second respiratory leveldetection collected by the collection unit, the informing unit generatesa display image indicating a change in the second respiratory level, andthe informing unit further displays the display image to the subject.14. The magnetic resonance imaging apparatus according to claim 13,wherein the informing unit generates the display image as an imageindicating changes in the first and second respiratory levels.
 15. Themagnetic resonance imaging apparatus according to claim 13, wherein thedetection unit controls the collection unit to collect the magneticresonance signal for second respiratory level detection more than oncein a cycle where the magnetic resonance signal for first respiratorylevel detection is collected.
 16. The magnetic resonance imagingapparatus according to claim 1, wherein the detection unit controls thecollection unit to collect the magnetic resonance signal for respiratorylevel detection at a timing different from that of the magneticresonance signal for imaging, the detection unit further detects arespiratory level of the subject based on the magnetic resonance signalfor respiratory level detection, the informing unit generates a displayimage indicating the latest respiratory level detected by the detectionunit and a maximum value of the respiratory levels detected by thedetection unit in a predetermined period, and the informing unit furtherdisplays the display image to the subject.
 17. A magnetic resonanceimaging apparatus comprising: a collection unit which applies a uniformstatic magnetic field to a subject and also applies a radio-frequencymagnetic field and a gradient magnetic field to the subject inaccordance with a predetermined pulse sequence to individually collecteach magnetic resonance signal from the subject in relation to each of aplurality of slabs; a imaging unit which images an imaging regioncontaining the plurality of slabs based on the collected magneticresonance signals; a unit which detects a respiratory level of thesubject; a unit which controls the collection unit to collect themagnetic resonance signal when the detected respiratory level fallswithin an allowable range that is set with respect to each of theplurality of slabs; and a unit which sets the single allowable rangethat is applied in common to each of the plurality of slabs based on therespiratory level detected before the collection in relation to thefirst slab in the plurality of slabs begins.
 18. The magnetic resonanceimaging apparatus according to claim 17, further comprising an informingunit which informs the subject of whether the detected respiratory levelfalls within the allowable range.
 19. The magnetic resonance imagingapparatus according to claim 17, further comprising a unit whichcorrects the magnetic resonance signal collected by the collection unitto reduce an influence of a fluctuation in the respiratory level. 20.The magnetic resonance imaging apparatus according to claim 18, whereinthe informing unit comprises: a generation unit which is arranged in asecond room different from a magnetically shielded first room where thecollection unit is arranged and generates an image indicating whetherthe detected respiratory level falls within the allowable range; atransmission unit which optically transmits the image from the secondroom to the first room; and a display unit which is arranged in thefirst room and displays the image transmitted through the transmissionunit to the subject.
 21. The magnetic resonance imaging apparatusaccording to claim 20, wherein the generation unit generates imageinformation indicative of the image, the transmission unit transmits theimage information by using an optical signal, and the display unitreproduces and displays the image based on the image information. 22.The magnetic resonance imaging apparatus according to claim 20, whereinthe generation unit generates the image as a visible light image, thetransmission unit transmits the visible light image, and the displayunit projects the visible light image to eyes of the subject.
 23. Adisplay apparatus that is used with a magnetic resonance imagingapparatus that visualizes a subject based on a magnetic resonance signalcollected from the subject when a respiratory level of the subject fallswithin an allowable range, comprising: a generation unit which generatesan image indicating whether the respiratory level of the subject fallswithin the allowable range; and a display unit which displays the imageto the subject.
 24. A control method of a magnetic resonance imagingapparatus, the apparatus comprising: a collection unit which applies auniform static magnetic field to a subject and also applies aradio-frequency magnetic field and a gradient magnetic field to thesubject in accordance with a predetermined sequence to collect amagnetic resonance signal from the subject; and a imaging unit whichimages the subject based on the magnetic resonance signal collected bythe collection unit, wherein the method comprises: detecting arespiratory level of the subject; informing the subject of whether thedetected respiratory levels falls within the allowable range; andcontrolling the collection unit and the imaging unit to collect themagnetic resonance signal and visualize the subject based on the thuscollected magnetic resonance signal when the detected respiratory levelfalls within the allowable range.
 25. A control method of a magneticresonance imaging apparatus, the apparatus comprising: a collection unitwhich applies a uniform static magnetic field to a subject and alsoapplies a radio-frequency magnetic field and a gradient magnetic fieldto the subject in accordance with a predetermined sequence toindividually collect each magnetic resonance signal from the subject inrelation to each of a plurality of slabs; and a imaging unit whichvisualizes an imaging region containing the plurality of slabs based onthe collected magnetic resonance signal, wherein the method comprises:detecting a respiratory level of the subject; controlling the collectionunit to collect the magnetic resonance signal when the detectedrespiratory level falls within an allowable range that is set withrespect to each of the plurality of slabs; and setting the singleallowable range that is applied in common to each of the plurality ofslabs based on the respiratory level detected before the collection withrespect to the first slab in the plurality of slabs begins.